Hydrographic & Oceanographic vessels

The Hydrographer has the survey vessels HNlMS Snellius and HNlMS Luymes available to conduct surveys.

Main tasks:

Civil hydrographic surveys of the Dutch Continental Shelf and the waters around the Netherlands Antilles and Aruba.
Military hydrographic surveys in the operation areas of the Royal Netherlands Navy in support of mineclearing operations and amphibious operations.

Civil hydrographic surveys of the Netherlands Continental Shelf (NCS) and the waters around the Netherlands Antilles and Aruba (NA&A).

In accordance with the annual survey planning the ships are deployed in certain areas, which are to be surveyed on regular basis.

The most vital shipping areas such as the Traffic Separation Schemes and the deep draught (23 m) entrance to Europort Rotterdam, receive most attention. The northern part of the Dutch Continental Shelf (160 M north of Den Helder) also gets the appropriate attention.
The waters around the NA&A can be surveyed within a lager timeframe due to the fact that the seafloor in these areas is very stable.

Military hydrographic surveys
Besides the gathering of data from the NCS and the NA&A, the military hydrographic survey task exists in the conduct of “out of area” surveys. Therefore the survey vessels can be deployed worldwide. Alone, or as part of a taskforce.

The survey vessels are also able to carry out meteorological observations

Secondary tasks
The following secondary tasks can be defined:

General military tasks
The survey vessels can be deployed for general military tasks such as ready duty ship, platform for the Naval Control of Shipping Organization (NCSO) and to assist in maritime scientific research on behave of the Minister of Defence.

Society tasks
Due to the fact that the ships spend most of their time at sea in the southern part of the NCS (an area with a high shipping density), they are able to rapidly respond to emergency situations at sea. In this way the ships contribute to the coastguard duties of the Royal Netherlands Navy. The ships will also act as platform for conducting meteorological observations.

To perform all these duties, the vessels are fitted with modern survey equipment.

During the survey the seabed is accurately charted and all wrecks, and obstructions over one metre, are detected with special sonar equipment.
Because all depths in the charts are related to MLLWS the measured water depth needs to be corrected with the tide (tidal reduction). Until 1998 solely tide gauges deployed on the seabed with navigation buoys attached were used. Nowadays in general a tidal model (Premo, developed by WL | Delft Hydraulics) is applied. The predicted water level, based on astronomical tides from the model, is corrected for meteorological conditions using measurements from fixed tide gauges maintained by the Directorate General for Public Works and Water management. In areas not covered by the Premo model or if there are no reliable fixed tide gauges available, tide gauges are still deployed on the seabed.
Hydrographically trained naval officers perform processing of the survey data.

The ships also carry survey motorboats and inflatable boats. These are used to survey shallow waters. In support of some military operations, landing beaches and the boat-lanes leading towards them can thus been surveyed in advance of amphibious operations.

RNlN Hydrographic service